12 THE FLOATING-MATTER OF THE AIR. 



tubes were cloudy, the cloudiness becoming denser on 

 the following days, while disks of Penicillium began 

 to form on the exposed surfaces. It was found ex- 

 ceedingly difficult to obtain a clear infusion of kidney. 

 The liquid, after it had passed through a dozen filters, 

 was still quite muddy. With considerable labour and 

 care, and by the employment of 200 filters, the mechani- 

 cally suspended matter was at length removed, and a 

 clear infusion obtained. It was introduced into its 

 case, to which three exposed tubes were attached, on 

 the 4th of January. On the 7th the latter were per- 

 ceptibly cloudy, on the 8th distinctly so, while specks 

 of mould rested upon them all. The protected tubes, on 

 the contrary, have for months maintained their trans- 

 parency undimmed.^ 



The entire number of experiments made to illustrate 

 the association of scattered light and Bacterial and 

 fungoid life are not here recounted. Whiting, for 

 example, may be added to the fish, and pork to the 

 flesh examined, while many of the other substances 

 have been tested oftener than I have thought it neces- 

 sary to record. The method of boiling was also varied 

 in a manner which may claim a passing reference here. 



§ 14. Boiling by an Internal Source of Heat 



Two large test-tubes were fixed air-tight in the 

 same case. On the 8th of November, after the floating 

 matter had subsided, infusions of hay and turnip were 

 introduced. Dipping deep into each infusion were two 

 tinned copper wires, connected below by a spiral of 



* Kidney has been mentioned by Dr. Bastian as a substance 

 with which he demonstrates the occurrence of spontaneous genera- 

 tion. He does not mention the extraordinary turbidity of the 

 infusion, which proved so troublesome to me. 



